In a linear amplification with nonlinear component (LINC) among the power amplification systems used for amplifying a transmit signal in a communication device or the like, after an input signal having an envelope variation has been converted into two constant envelope signals (intermediate signals) having a phase difference corresponding to the amplitude of the input signal, the respective envelope signals are amplified by a nonlinear amplifier. Then, the amplified constant envelope signals are vectorially added to obtain an amplified input signal. According to this system, because the nonlinear amplifier has only to amplify the constant envelope signals, a power amplification efficiency may be improved (for example, refer to Patent Document 1).    Patent Document 1: JP 06-22302 B